Method for intra prediction and device therefor

1. An image decoding method comprising: setting a first candidate intra prediction mode corresponding to a left candidate block on the basis of a location of the left candidate block adjacent to a left side of a current block; setting a second candidate intra prediction mode corresponding to an upper candidate block on the basis of a location of the upper candidate block adjacent to an upper portion of the current block; generating a candidate mode list including a plurality of candidate intra prediction modes on the basis of the first candidate intra prediction mode and the second candidate intra prediction mode; setting one candidate intra prediction mode as an intra prediction mode of the current block among a plurality of candidate intra prediction modes constituting the candidate mode list, and performing an intra prediction on the current block on the basis of the determined intra prediction mode to generate a prediction block corresponding to the current block; generating a reconstructed block on the basis of the prediction block, wherein the first candidate intra prediction mode or the second candidate intra prediction mode is set to DC mode when the left candidate block or the upper candidate block is not available; and wherein the setting of the first candidate intra prediction mode comprises determining that the left candidate block is not available when the left candidate block is located outside a current picture to which the current block belongs and sets the first candidate intra prediction mode to a DC mode, and wherein the setting of the second candidate intra prediction mode comprises determining that the upper candidate block is not available when the upper candidate block is located outside the current picture and sets the second candidate intra prediction mode to the DC mode.

2. The image decoding method of claim 1 , wherein the setting the first candidate intra prediction mode comprises determining that the left candidate block is not available when the left candidate block is located outside a coding tree block (CTB) that represents the largest coding block to which the current block belongs and sets the first candidate intra prediction mode to DC mode, the setting the second candidate intra prediction mode comprises determining that the upper candidate block is not available when the upper candidate block is located outside the CTB to which the current block belong and sets the second candidate intra prediction mode to DC.

3. The image decoding method of claim 1 : wherein the setting of the first candidate intra prediction mode comprises determining that the left candidate block is not available when the left candidate block is located outside a current slice to which the current block belongs and setting the first candidate intra prediction mode to a DC mode, and wherein the setting of the second candidate intra prediction mode comprises determining that the upper candidate block is not available when the upper candidate block is located outside the current slice and setting the second candidate intra prediction mode to the DC mode.

4. The image decoding method of claim 1 : wherein the setting of the first candidate intra prediction mode comprises determining that the left candidate block is not available when a prediction mode of the left candidate block is not an intra mode and sets the first candidate intra prediction mode to a DC mode, and wherein the setting of the second candidate intra prediction mode comprises determining that the upper candidate block is not available when a prediction mode of the upper candidate block is not the intra mode and setting the second candidate intra prediction mode to the DC mode.

5. The image decoding method of claim 1 , wherein setting the first candidate intra prediction mode comprises: determining that the left candidate block is not available when the left candidate block is located outside a current tile to which the current block belongs, and setting the first candidate intra prediction mode to a DC mode, and wherein setting the second candidate intra prediction mode comprises: determining that the upper candidate block is not available when the upper candidate block is located outside a current tile to which the current block belongs, and setting the second candidate intra prediction mode to the DC mode.

6. The image decoding method of claim 1 , wherein the first candidate intra prediction mode is a prediction mode corresponding to a block located in an uppermost portion among left neighboring blocks located to a left side of the current block and the second candidate intra prediction mode is a prediction mode corresponding to a block located in a leftmost portion among upper neighboring blocks located to a upper side of the current block.

7. The image decoding method of claim 1 , wherein the intra prediction mode of the current block is set using information transmitted from an encoding apparatus indicating one candidate intra prediction mode in the candidate mode list.